I tried 3 triggers once and it ended in utter disaster. It was in a 100 gallon tank and I went with the wrong triggers: Clown, Undulated, and Picasso.
With that said, there are some species that are considered a bit more docile like the Niger, Pink Tail, Blue Throat, and Cross Hatch. But I believe that even the more docile Triggers can have a personality that wants to wreak havoc based on the individual. You might want to consider one trigger and some other tough fish like a puffer, and a Snow Flake Eel.
Consequently, if I was to have one trigger it would be an Assassi. They don't pop up too often, but they are more vibrant and have a more "Submarine" shape than a Picasso.